1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a delayed acknowledgement transmission method and apparatus for improving communication performance of a system and a terminal by delaying ACKnowledgement (ACK) transmission of the terminal in a handover procedure.
2. Description of the Related Art
In a cellular mobile communication system, as a user moves to a cell edge in a cellular mobile communication system, a terminal releases a connection to a serving cell, or a source cell, and establishes a new connection to a neighboring cell, or a target cell. Such a process, in which the terminal switches the connection from one cell to another according to the terminal's roaming or communication environment change, is referred to as a handover.
FIG. 1 is a diagram illustrating a principle of a handover procedure according to the related art.
Referring to FIG. 1, a mobile communication system includes Mobile Equipment (ME) 100, a router 130, a gateway 140, a Source evolved Node B (SeNB) 115 managing a source cell 110, and a Target eNB (TeNB) 125 managing a target cell 120. The SeNB is also referred to as a serving eNB. The terms “SeNB” and “serving eNB” are used interchangeably herein. The source cell is also referred to as a service cell. The terms “source cell” and “serving cell” are used interchangeably herein.
It is assumed that the ME 100, which has received a data segment from a server 150 via the gateway 140, router 130, and SeNB 115, is transmitting an ACK corresponding to the data segment, before a handover takes place. The ME 100 moves out of the source cell 110 and enters the target cell 120. At this time, the ME 100 receives a Handover Command from the SeNB 115 and performs handover by releasing the connection to the SeNB 115 and establishing a new connection to the TeNB 125.
In the handover procedure of the related art, the ME 100 releases the connection to the SeNB 115 upon receipt of the handover command and sends a handover confirm message to the target to the TeNB 125. If the handover confirm message is received, the TeNB 125 begins path switching. The packets (data segments) arrived at the SeNB 115 after it has transmitted the handover command to the ME 100 are stored at the buffer of the SeNB 115 and are forwarded to the TeNB 125 after the completion of the path switching.
In this process, the same packets are passing the router 130 of the core network twice for a very short time (i.e., twice queuing) thereby causing instant overload. This increases the queue size of the router 130 abruptly, resulting in a packet processing delay or an increase of packet loss probability due to overflow. The packet processing delay or packet loss becomes the reason of the Slow Start and Window Halving in Transmission Control Protocol (TCP), resulting in degradation of TCP performance. This problem becomes more significant in networks with a high density of MEs or high mobility MEs.
As shown in FIG. 1, when forwarding data from the SeNB 115 to the TeNB 125 in a handover procedure, the original packets transmitted by the server 150 and the duplicate packets forwarded by the SeNB 115 are accumulated in the queue of the router 130 simultaneously. As a consequence, the queue of the router 130 overflows instantly so as to cause packet processing delay or packet loss, resulting in TCP timeout.
Therefore, a need exists for an acknowledgement transmission method and apparatus capable of avoiding performance degradation of a router, packet processing delay, and packet loss.